Optically active C-3-symmetric triarylphosphines in asymmetric allylations

A new class of optically active, monodentate, C-3-symmetric Ligands for asy mmetric catalysis, 1-3, were prepared via routes involving asymmetric reduc tion of aryl ketones (Schemes 1-3). Single crystal X-ray structures of tran s-PdCl2(phosphine)(2) complexes of Ligands 1a, 2a and 3a showed that the li gands do not adopt perfect C3-symmetric conformations in the solid state; i n fact, all three have one aromatic ring lying 'face-on' to the metal. Circ ular dichroism studies of the same complexes provided some evidence for an aromatic ordering effect for complex 22, but none for 21 and 23. Palladium catalyzed allylation reactions using ligands 1-3 showed that encouraging en antioselectivities could be obtained, particularly for cyclic, allylic subs trates. (C) 2001 Elsevier Science Ltd. All rights reserved.